For decoder side MV derivation and refinement

ABSTRACT

In a method for video decoding in a decoder, a first motion vector and a second motion vector for a first block in a current picture are received. The first motion vector is indicative of a first reference block in a first picture. The second motion vector is indicative of a second reference block in a second picture. A bilateral template is generated based on a weighted combination of the first and the second reference blocks. A refined first motion vector is determined based on the bilateral template and reference blocks in the first picture. A refined second motion vector is determined based on the bilateral template and reference blocks in the second picture. An initial motion vector of a second block that is coded after the first block is determined according to at least one of the first motion vector and the second motion vector for the first block.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 62/693,060, “IMPROVEMENT FOR DECODER SIDE MVDERIVATION AND REFINEMENT” filed on Jul. 2, 2018, which is incorporatedby reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videocoding. In some examples, an apparatus includes receiving circuitry andprocessing circuitry.

According to an aspect of the current disclosure, a method for videodecoding in a decoder is provided. In the disclosed method, a firstmotion vector and a second motion vector are received for a first blockin a current picture of a video. The first motion vector is indicativeof a first reference block in a first picture, and the second motionvector is indicative of a second reference block in a second picture.The current picture is between the first picture and the second picturein the video. Next, a bilateral template is generated based on aweighted combination of the first reference block and the secondreference block. A refined first motion vector is subsequentlydetermined based on the bilateral template and a first set of referenceblocks in the first picture. The refined first motion vector indicates afirst refined reference block in the first picture. Further, a refinedsecond motion vector is determined based on the bilateral template and asecond set of reference blocks in the second picture. The refined secondmotion vector indicates a second refined reference block in the secondpicture. An initial motion vector of a second block that is coded afterthe first block is determined according to at least one of the firstmotion vector and the second motion vector for the first block.

In some embodiments, the first block is included in a candidate list ofcandidate motion vector predictors for the second block during a processof constructing the candidate list. The first set of reference blocksincludes the first reference block and eight reference blocks atdifferent positions of the first reference block in the first picture,and the second set of reference blocks includes the second referenceblock and eight reference blocks at different positions of the secondreference block in the second picture.

In some embodiments, the determining the refined first motion vectorincludes determining a first minimum cost measure in the first set ofreference blocks, and the determining the refined second motion vectorincludes determining a second minimum cost measure in the second set ofreference blocks. The cost measure includes at least one of a sum ofabsolute difference (SAD) measure, a mean square error (MSE) measure, amean absolute difference (MAD) measure, or a matching-pixel count (MPC)measure.

In some embodiments, the first block is reconstructed according to thefirst refined motion vector that is indicative of the first refinedreference block in the first picture, and the second refined motionvector that is indicative of the second refined reference block in thesecond picture.

In some embodiments, a refinement interpolation filter is applied duringdetermination of the refined first or second motion vector. Therefinement interpolation filter has a filter length of Tap__(MC-DMVR). Afinal motion compensation interpolation filter is applied duringreconstruction of the first block. The final motion compensationinterpolation filter has a filter length of Tap__(SR). In an example,2×SR+Tap__(MC-DMVR)/2+Tap__(SR)/2=Tap__(MC), where the SR is a searchrange to determine the first set of reference blocks or the second setof reference blocks, respectively, and the Tap__(MC) is a filter lengthof a regular motion compensation interpolation filter that is appliedwhen the first block is reconstructed based on the first motion vectorand the second motion vector.

In some embodiments, the refinement interpolation filter has a verticalfilter length and a horizontal filter length, and the vertical filterlength is different from the horizontal filter length.

In an embodiment, the search range to determine the first or second setof reference blocks is an adaptive search range that is defined based ona block size of the first block. In an embodiment, a size of the searchrange is defined based on an area of the first block.

According to another aspect of the present disclosure, an apparatus isprovided. The apparatus has processing circuitry. The processingcircuitry is configured to perform the disclosed method for videocoding.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo coding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 shows a schematic diagram that illustrates a decoder side motionvector refinement (DMVR) mode according to an embodiment.

FIG. 9 shows a schematic diagram that illustrates a coding and decodingorder of coding blocks (CUs) according to an embodiment.

FIG. 10 shows a schematic diagram that illustrates pipeline stagesassociated with the DMVR mode according to an embodiment.

FIG. 11 shows a schematic diagram that illustrates an improved DMVR modeaccording to an embodiment.

FIG. 12 shows a schematic diagram that illustrates an efficient pipelineassociated with the improved DMVR mode according to one embodiment.

FIG. 13 shows a flow chart outlining a decoding process according to anembodiment.

FIG. 14 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

FIG. 8 shows a schematic diagram that illustrates a decoder side motionvector refinement (DMVR) mode according to an embodiment. Comparing tothe merge mode that is shown in FIG. 1, the DMVR mode is another tool toimprove/refine a motion vector (MV) based on starting points. The DMVRmode provides a bi-prediction operation. In the bi-prediction operation,in order to predict one block region, two prediction (or reference)blocks that are formed by using a first MV of list0 and a second MV oflist1 respectively, are combined to form a single prediction signal(bilateral template). In the DMVR method, the two motion vectors of thebi-prediction are further refined by a bilateral template matchingprocess. The bilateral template matching process is applied in thedecoder to perform a distortion-based search between the bilateraltemplate and the reference samples (blocks) in the reference pictures toobtain a refined MV without transmission of additional motioninformation.

As shown in FIG. 8, a current block (802) can be predicted according tothe DMVR mode in the decoder side. The DMVR mode can predict the currentblock (802) in two steps. In step 1, a bilateral template (804) isgenerated as a weighted combination (i.e., average) of the twoprediction (or reference) blocks (806) and (808), according to a firstinitial (MV0) of list0 and a second initial (MV1) of list1,respectively. In step 2, the bilateral template matching operationcalculates cost measures between the generated template (804) andreference blocks in sample regions (around the initial prediction block)in reference pictures. For example, a sample region (810) of a firstreference picture and a sample region (812) of a second referencepicture are included in FIG. 8. Reference blocks in sample region (810)can be included in list0 and reference blocks in sample region (812) canbe included in list1. According to Joint Exploration Model (JEM), nineMV candidates can be included in each of list0 and list1. In each oflist0 and list1, the nine MV candidates include the original MV, such as(MV0) in the list0, and 8 surrounding MVs with a one luma sample offsetto the original MV in either the horizontal or vertical direction, orboth. Each of the nine MV candidates in either list0 or list1 isindicative of a respective reference block.

In step 2, the bilateral template matching operation calculates a costmeasure between the generated bilateral template (804) and each of thenine reference blocks in list0 and list1, respectively. For example, thebilateral template matching operation can obtain nine cost measuresbased on the bilateral template (804) and the nine reference blocks inthe list0. In each of list0 and list1, a reference block that yields aminimum template cost is determined as an updated (refined) referenceblock, and a MV that is indicative of the updated reference block isconsidered as a refined (final) MV. The updated MV further replaces theinitial MV to predict the current block (802). For example, a firstrefined (final) (MV0′) is generated in list0 and a second refined(final) (MV1′) is generated in list1, respectively. The first refined(MV0′) is indicative of a first refined reference block and the secondrefined (MV1′) is indicative a second refined reference block. The firstrefined reference block and the second refined reference block furthercan be applied to generate the final bi-prediction result to predict thecurrent block (802).

In some embodiments, a sum of absolute differences (SAD) is used as thecost measure. In other embodiments, the cost measure can include a meansquare error (MSE) measure, a mean absolute difference (MAD) measure, amatching-pixel count (MPC) measure, or the like.

In some embodiments, the DMVR mode can be applied for the merge mode ofbi-prediction with one MV from a reference picture in the past andanother from a reference picture in the future, without the transmissionof additional syntax elements.

FIG. 9 shows a schematic diagram that illustrates a coding and decodingorder of coding blocks (CUs) according to an embodiment. In FIG. 9, aspatial relationship between a current coding block and a previous blockthat is immediately coded before the current block are shown in examples(901) and (902). The decoding order is known by both encoder anddecoder. When decoding the current block, such as a current block (908)in the example (902), normally MVs of the current block's spatialneighbors will be used as predictors for coding a MV of the currentblock (908). For example, MVs from the blocks decoded in the order of 0,1, 2 in the example (902) can be used as predictor candidates for thecurrent block (908) in the example (902). In both examples (901) and(902), a previous block (e.g., a block (906) in the example (901), and ablock (910) in the example (902)) can be included in a candidate list ofcandidate MV predictors to predict a current block (e.g., a block (904)in the example (901), and a block (908) in the example (902)). Inaddition, a position of the previous block changes as a position of thecurrent block changes. For example, the previous block and the currentblock are aligned in a diagonal direction in the example (901), and theprevious block and the current block are aligned side to side in theexample (902).

FIG. 10 shows a schematic diagram that illustrates pipeline stagesassociated with the DMVR mode according to an embodiment. The DMVR modecan perform the following three processes: (1) an initial MV (MV_init)is parsed and a reference blocks identified by the initial MV isprefetched for a current block; (2) the MV_init is refined to determinea final MV (MV_final) or refined MV through the bilateral templatematching operation for the current block; and (3) motion compensation(MC) is performed with MV_final for the current block to reconstruct thecurrent block. In the second process, a final or refined MV can bedetermined for each of one or more initial motion vectors. For example,a first motion vector that indicates a first reference block in a firstpicture and a second motion vector that indicates a second referenceblock in a second picture. In the third process, motion compensation canbe performed based on the one or more final or refined motion vector.

As shown in FIG. 10, a coding unit 0 (CU0) is processed by the threeprocesses at three time stages, e.g., from T0 to T2. In hardwarepipeline design, it is more efficient to have each process workconsecutively in different time stages so that within a certain periodmore CUs can be processed. However, if a final MV for CU0 is used as apredictor to generate an initial MV for coding unit 1 (CU1), the firstprocess of parsing the initial MV and prefetching the reference blockthat is identified by the parsed initial MV for CU1 cannot be starteduntil the MV_final of CU0 is determined in the second process.Therefore, the first process for CU1 cannot be started at T1. Similarly,coding units 2 (CU2) and 3 (CU3) cannot be started at T3 and T5,respectively, for example when a final MV for CU1 is used as a predictorto generate an initial MV for CU2, and a final MV for CU2 is used as apredictor to generate an initial MV for CU3. As described above, theprocesses to be performed on subsequent coding units in the DMVR moderequire access to a reconstructed neighboring block. This results indelays in starting the processes for the subsequent coding units toallow time for the required neighboring blocks to be reconstructed.

In FIG. 11, an improved DMVR mode is provided according to oneembodiment. In the improved DMVR mode, when the previously decoded block(CU_prev), that is coded right before the current block, is included inthe candidate list of candidate MV predictors for the current blockduring the process of constructing the candidate list (e.g., asdescribed above with respect to FIG. 8), an MV_init (i.e., MV beforerefinement) rather than a final, or refined, MV (i.e., MV_final, or MVafter refinement) for the CU_prev is applied as the candidate.Accordingly, the MV parsing process for the current block (CU_cur)and/or prefetching of reference samples for the CU_cur does not need towait until the MV refinement of CU_prev to finish. As shown in FIG. 11,a current block can be CU1, and a previously coded block can be CU0. Inthe improved DMVR mode, when CU0 is included in the candidate list ofcandidate MV predictors for CU1 during the process of constructing thecandidate list, an MV_init rather than MV_final of CU0 can be applied asthe candidate to determine an MV_init of the current block CU1.Similarly, in the improved DMVR mode, when CU1 is included in thecandidate list of MV predictors for CU2 during the process ofconstructing the candidate list, an MV_init rather than MV_final for CU1can be applied as the candidate to determine an MV_init for the currentblock CU2. As noted above, in the second process, a final or refined MVcan be determined for each of one or more initial motion vectors. Forexample, a first motion vector that indicates a reference block in afirst picture and a second motion vector that indicates a referenceblock in a second picture. In the third process, motion compensation canbe performed based on the one or more final or refined motion vector.

FIG. 12 shows a schematic diagram that illustrates a more efficientpipeline associated with the improved DMVR mode according to anembodiment. As shown in FIG. 12, at T0, the MV_init for CU0 isdetermined. At T2, MV_init for CU0 can be further applied to determinethe MV_init for CU1 if the CU0 is in the candidate list of thepredictors for CU1. In addition, the MV_init for CU0 is refined throughthe DMVR mode at T2. At T2, a motion compensation based on the MV_finalfor CU0 can be applied to reconstruct the CU0. In the meanwhile, theMV_init for CU1 is refined through the DMVR mode at T2. Similar timingsfor the processes can be applied to CU2, CU3, and so on, as illustratedin FIG. 12. By introduction of the improved DMVR mode, an efficientpipeline can be obtained and pipeline delay can be prevented or reduced.

In some embodiments, in order to keep a memory bandwidth requirement ofthe improved DMVR mode the same as a regular inter mode, for example asillustrated in FIG. 1, interpolation filters that are used in an MVrefinement process and in a final motion compensation interpolationprocess can be designed with a special number of taps so that afollowing condition (1) is met2×SR+Tap_ _(MC-DMVR)/2+Tap_ _(SR)/2==Tap_ _(MC)  (1)where SR is a search range (in pixels) in the MV refinement process,Tap__(MC-DMVR) and Tap__(SR) are filter lengths (i.e., number of filtertaps) of the interpolation filters applied during the MV refinementprocess of the improved DMVR mode and during the final motioncompensation interpolation process for the improved DMVR mode,respectively. The Tap__(MC) represents a filter length of aninterpolation filter used in a motion compensation interpolation for theregular inter mode that is illustrated in FIG. 1.

In some embodiments, the search range SR can be 2. The Tap__(SR) can bein a range from two to eight. Further, Tap__(MC) can be eight, and theTap__(MC-DMVR) is a variable that is defined by the condition (1)mentioned above.

In the disclosed improved DMVR mode, in order to reduce memory access bythe DMVR mode, different taps of interpolation filters can be appliedfor vertical and horizontal interpolation during the refinement process.In an embodiment, a number of taps for a vertical interpolation (i.e.,the vertical filter length) is smaller (shorter) than a number of tapsfor a horizontal interpolation (i.e., the horizontal filter length). Forexample, the vertical interpolation can use 6-tap filters while thehorizontal interpolation can use 8-tap filters. In another embodiment,the vertical filter may be asymmetric. For example, a number of tapsabove a to-be-interpolated position can be M, a number of taps below theto-be-interpolated position can be N, and M may be smaller than N. Thesum of M and N may be the same or different from the number of taps usedin the horizontal interpolation filter.

In the disclosed improved DMVR mode, in order to reduce memory access bythe DMVR mode, an adaptive search range can be applied during the MVrefinement of the improved DMVR mode. In an embodiment, the search rangecan be determined based on a block size of the current block. When theblock size of the current block is smaller than a threshold, a firstsearch range is used. When the block size of the current block is largeror equal to the threshold, a second search range is used. Thethreshold(s) and the value(s) of search range(s) may be predefined orsignaled in bitstreams, such as in an SPS, PPS or slice header. In anexample, the threshold of the block size can be defined as 64 pixels.Accordingly, below the threshold, a 1-pixel search range is used.Otherwise, a 2-pixel search range is used. In another example, more thanone threshold and more than two search ranges can be applied.

In another embodiment, the search range can be a rectangle, where awidth and a height of the search rectangle are dependent on a width anda height of the current block. In one example, the width and the heightof the search rectangle is proportional to the width and height of thecurrent block. For example, when the current block has a width of 16 anda height of eight, the search range has a width of one and a height of ½in terms of pixels. Similarly, a 32×64 block size can correspond to asearch range with a width equal to two and a height equal to four.

In another example, when the width of the current block is greater (orsmaller) than a predefined or signaled threshold, the width of thesearch rectangle is equal to a first value. Otherwise, the width of thesearch rectangle is equal to a second value. For example, when thecurrent block has a width less than a threshold of eight, the searchrange has a width that is equal to the first value of zero. Otherwise,the search range has a width equal to the second value of two. When thecurrent block has a width larger than a threshold 64, the search rangecan have a width equal to the first value of zero. Otherwise, the searchrange has a width equal to the second value of two.

In yet another example, when the height of the current block is greater(or smaller) than a predefined or a signaled threshold, the height ofthe search rectangle is equal to a first value. Otherwise the height ofthe search rectangle is equal to a second value. For example, when thecurrent block has a height less than a threshold of eight, the searchrange has a height that is equal to the first value of zero. Otherwise,the search range has a height equal to the second value of two. When thecurrent block has a height larger than a threshold of 64, the searchrange can have a height equal to the first value of zero. Otherwise, thesearch range has a height equal to the second value of two.

In yet another embodiment, the size (area) of the search range isdetermined based on the area of the current block (i.e., the totalnumber of pixels in the current block). In an example, when the area ofthe current block is greater (or smaller) than a predefined or signaledthreshold, the area of the search rectangle is equal to a first value.Otherwise the area of the search rectangle is equal to a second value.For example, when the current block has an area less than a threshold of64, the search rectangle can have an area equal to the first value ofzero, otherwise the search rectangle can have an area equal to thesecond value of four. When the area of current block is greater than athreshold of 4096, the search rectangle can have an area equal to thefirst value of zero, otherwise the search rectangle has an area equal tothe second value of 4.

In another example, the search range has a square shape where the lengthof (number of pixels along) each side is a square root of the arearounded to the nearest integer. For example, the area of the searchrange (in terms of pixels) can be 4, 16, etc.

In yet another example, the width to height ratio of the search range isthe same as the width to height ratio of the current block. The widthand height of the search range are calculated from the area of thesearch range and rounded to the nearest integer values. For example, thewidth to height ratio could be 1/32, 1/16, ⅛, ¼, ½, 1, 2, 4, 8, 16, or32.

FIG. 13 shows a flow chart outlining a process (1300) according to anembodiment of the disclosure. The process (1300) can be used in thereconstruction of a block coded in intra mode, so to generate aprediction block for the block under reconstruction. In variousembodiments, the process (1300) are executed by processing circuitry,such as the processing circuitry in the terminal devices (210), (220),(230) and (240), the processing circuitry that performs functions of thevideo encoder (303), the processing circuitry that performs functions ofthe video decoder (310), the processing circuitry that performsfunctions of the video decoder (410), the processing circuitry thatperforms functions of the intra prediction module (452), the processingcircuitry that performs functions of the video encoder (503), theprocessing circuitry that performs functions of the predictor (535), theprocessing circuitry that performs functions of the intra encoder (622),the processing circuitry that performs functions of the intra decoder(772), and the like. In some embodiments, the process (1300) isimplemented in software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1300). The process starts at (S1301) and proceeds to(S1310).

At step (S1310), a first motion vector and a second motion vector arereceived, or otherwise determined, for a first block in a currentpicture of a video. The first motion vector is indicative of a firstreference block in a first picture, and the second motion vector isindicative of a second reference block in a second picture. The currentpicture being between the first picture and the second picture in thevideo sequence. In some embodiments, the first motion vector can be MV0and the second motion vector can be MV1 that are illustrated withreference to FIG. 8.

At step (S1320), a bilateral template can be generated based on thefirst reference block and the second reference block. For example, thebilateral template can be generated based on a weight combination of thefirst and second reference blocks. For example, a first reference block(806), a second reference block (808), and a bilateral template (804)are illustrated in FIG. 8.

At step (S1330), a refined first motion vector is determined. Therefined first motion vector can be determined based on the bilateraltemplate and a first set of reference blocks in the first picture. Therefined first motion vector indicates a first refined reference block inthe first picture. A refined second motion vector is also determined.The refined second motion vector can be based on the bilateral templateand a second set of reference blocks in the second picture. The refinedsecond motion vector indicates a second refined reference block in thesecond picture. For example, a refined first motion vector (MV0′), arefined second motion vector (MV1′), a first refined reference block(814), and a second refined reference block (816) are illustrated inFIG. 8.

In step (S1340) of the process 1300, an initial motion vector of asecond block is determined. The initial motion vector of the secondblock can be determined according to at least one of the first motionvector and the second motion vector for the first block. The secondblock is coded after the first block. Accordingly, the initial motionvector of the second block can be determined without waiting for therefined first and/or second motion vectors of the first block to bedetermined. For example, a second block (CU1) and a first block (CU0)are illustrated in FIG. 12.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 14 shows a computersystem (1400) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 14 for computer system (1400) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1400).

Computer system (1400) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1401), mouse (1402), trackpad (1403), touchscreen (1410), data-glove (not shown), joystick (1405), microphone(1406), scanner (1407), camera (1408).

Computer system (1400) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1410), data-glove (not shown), or joystick (1405), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1409), headphones(not depicted)), visual output devices (such as screens (1410) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1400) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1420) with CD/DVD or the like media (1421), thumb-drive (1422),removable hard drive or solid state drive (1423), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1400) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1449) (such as, for example USB ports of thecomputer system (1400)); others are commonly integrated into the core ofthe computer system (1400) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1400) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1440) of thecomputer system (1400).

The core (1440) can include one or more Central Processing Units (CPU)(1441), Graphics Processing Units (GPU) (1442), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1443), hardware accelerators for certain tasks (1444), and so forth.These devices, along with Read-only memory (ROM) (1445), Random-accessmemory (1446), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1447), may be connectedthrough a system bus (1448). In some computer systems, the system bus(1448) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1448),or through a peripheral bus (1449). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1441), GPUs (1442), FPGAs (1443), and accelerators (1444) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1445) or RAM (1446). Transitional data can be also be stored in RAM(1446), whereas permanent data can be stored for example, in theinternal mass storage (1447). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1441), GPU (1442), massstorage (1447), ROM (1445), RAM (1446), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1400), and specifically the core (1440) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1440) that are of non-transitorynature, such as core-internal mass storage (1447) or ROM (1445). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1440). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1440) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1446) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1444)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: receiving a first motion vector and a second motion vectorfor a first block in a current picture of a video, the first motionvector being indicative of a first reference block in a first picture,and the second motion vector being indicative of a second referenceblock in a second picture; the current picture being between the firstpicture and the second picture in the video; generating a bilateraltemplate based on a weighted combination of the first reference blockand the second reference block; determining, by applying a refinementinterpolation filter, a refined first motion vector based on thebilateral template and a first set of reference blocks in the firstpicture, the refined first motion vector indicating a first refinedreference block in the first picture; determining a refined secondmotion vector based on the bilateral template and a second set ofreference blocks in the second picture, the refined second motion vectorindicating a second refined reference block in the second picture;determining an initial motion vector of a second block that is codedafter the first block according to at least one of the first motionvector and the second motion vector for the first block; andreconstructing, by applying a final motion compensation interpolationfilter, the first block according to (i) the first refined motion vectorthat is indicative of the first refined reference block in the firstpicture; and (ii) the second refined motion vector that is indicative ofthe second refined reference block in the second picture, wherein therefinement interpolation filter and the final motion compensationinterpolation filter have respective filter lengths determined based ona search range to determine the first set of reference blocks or thesecond set of reference blocks, and a filter length of a regular motioncompensation interpolation filter that is applied when the first blockis reconstructed based on the first motion vector and the second motionvector.
 2. The method of claim 1, wherein the first block is included ina process of constructing a candidate list of candidate motion vectorpredictors for the second block.
 3. The method of claim 1, wherein thefirst set of reference blocks includes the first reference block andeight reference blocks at different positions of the first referenceblock in the first picture, and the second set of reference blocksincludes the second reference block and eight reference blocks atdifferent positions of the second reference block in the second picture.4. The method of claim 1, wherein the determining the refined firstmotion vector includes determining a first minimum cost measure in thefirst set of reference blocks, and the determining the refined secondmotion vector includes determining a second minimum cost measure in thesecond set of reference blocks.
 5. The method of claim 4, wherein thecost measure comprises at least one of a sum of absolute difference(SAD) measure, a mean square error (MSE) measure, a mean absolutedifference (MAD) measure, or a matching-pixel count (MPC) measure. 6.The method of claim 1, wherein the filter length of the refinementinterpolation filter is Tap__(MC-DMVR), and the filter length of thefinal motion compensation interpolation filter is Tap__(SR).
 7. Themethod of claim 6, wherein2×SR+Tap_ _(MC-DMVR)/2+Tap_ _(SR)/2=Tap_ _(MC), the SR is the searchrange to determine the first set of reference blocks or the second setof reference blocks, and the Tap__(MC) is the filter length of theregular motion compensation interpolation filter that is applied whenthe first block is reconstructed based on the first motion vector andthe second motion vector.
 8. The method of claim 6, wherein therefinement interpolation filter has a vertical filter length and ahorizontal filter length, and the vertical filter length is differentfrom the horizontal filter length.
 9. The method of claim 7, wherein thesearch range to determine the first or second set of reference blocks isan adaptive search range that is defined based on a block size of thefirst block.
 10. The method of claim 7, wherein a size of the searchrange is defined based on an area of the first block.
 11. An apparatus,comprising: processing circuitry configured to: receive a first motionvector and a second motion vector for a first block in a current pictureof a video, the first motion vector being indicative of a firstreference block in a first picture, and the second motion vector beingindicative of a second reference block in a second picture, the currentpicture being between the first picture and the second picture in thevideo; generate a bilateral template based on a weighted combination ofthe first reference block and the second reference block; determine, byapplication of a refinement interpolation filter, a refined first motionvector based on the bilateral template and a first set of referenceblocks in the first picture, the refined first motion vector indicatinga first refined reference block in the first picture; determine arefined second motion vector based on the bilateral template and asecond set of reference blocks in the second picture, the refined secondmotion vector indicating a second refined reference block in the secondpicture; determine an initial motion vector of a second block that iscoded after the first block according to at least one of the firstmotion vector and the second motion vector for the first block; andreconstruct, by application of a final motion compensation interpolationfilter, the first block according to (i) the first refined motion vectorthat is indicative of the first refined reference block in the firstpicture, and (ii) the second refined motion vector that is indicative ofthe second refined reference block in the second picture, wherein therefinement interpolation filter and the final motion compensationinterpolation filter have respective filter lengths determined based ona search range to determine the first set of reference blocks or thesecond set of reference blocks, and a filter length of a regular motioncompensation interpolation filter that is applied when the first blockis reconstructed based on the first motion vector and the second motionvector.
 12. The apparatus of claim 11, wherein the first block isincluded in a process of constructing a candidate list of candidatemotion vector predictors for the second block.
 13. The apparatus ofclaim 11, wherein the processing circuitry is further configured to:determine the refined first motion vector based on a first determinationthat the refined first motion vector is associated with a first minimumcost measure in the first set of reference blocks, and determine therefined second motion vector based on a second determination that therefined second motion vector is associated with a second minimum costmeasure in the second set of reference blocks.
 14. The apparatus ofclaim 11, wherein the filter length of the refinement interpolationfilter is Tap__(MC-DMVR), and the filter length of the final motioncompensation interpolation filter is Tap__(SR).
 15. The apparatus ofclaim 11, wherein2×SR+Tap_ _(MC-DMVR)/2+Tap_ _(SR)/2=Tap_ _(MC), the SR is the searchrange to determine the first set of reference blocks or the second setof reference blocks, and the Tap__(MC) is the filter length of theregular motion compensation interpolation filter that is applied whenthe first block is reconstructed based on the first motion vector andthe second motion vector.
 16. The apparatus of claim 14, wherein therefinement interpolation filter has a vertical filter length and ahorizontal filter length, and the vertical filter length is differentfrom the horizontal filter length.
 17. The apparatus of claim 15,wherein the search range to determine the first or second set ofreference blocks is an adaptive search range that is defined based on ablock size of the first block.
 18. The apparatus of claim 15, wherein asize of the search range is defined based on an area of the first block.19. A non-transitory computer-readable medium storing instructions whichwhen executed by a computer for video decoding cause the computer toperform: receiving a first motion vector and a second motion vector fora first block in a current picture of a video, the first motion vectorbeing indicative of a first reference block in a first picture, and thesecond motion vector being indicative of a second reference block in asecond picture; the current picture being between the first picture andthe second picture in the video; generating a bilateral template basedon a weighted combination of the first reference block and the secondreference block; determining, by applying a refinement interpolationfilter, a refined first motion vector based on the bilateral templateand a first set of reference blocks in the first picture, the refinedfirst motion vector indicating a first refined reference block in thefirst picture; determining a refined second motion vector based on thebilateral template and a second set of reference blocks in the secondpicture, the refined second motion vector indicating a second refinedreference block in the second picture; determining an initial motionvector of a second block that is coded after the first block accordingto at least one of the first motion vector and the second motion vectorfor the first block; and reconstructing, by applying a final motioncompensation interpolation filter, the first block according to (i) thefirst refined motion vector that is indicative of the first refinedreference block in the first picture; and (ii) the second refined motionvector that is indicative of the second refined reference block in thesecond picture, wherein the refinement interpolation filter and thefinal motion compensation interpolation filter have respective filterlengths determined based on a search range to determine the first set ofreference blocks or the second set of reference blocks, and a filterlength of a regular motion compensation interpolation filter that isapplied when the first block is reconstructed based on the first motionvector and the second motion vector.